The invention relates to a rotatable supporting element. The supporting elements may be supported at both ends, as in the case, for example, of winding shafts, winding pins or supporting pipes, as well as only at one end, as in the case, for example, of winding heads. The supporting function can be accomplished with or without clamping devices in the usual types of construction.
Generic supporting elements consist at least of a supporting body which, because of the supporting function, is manufactured from a material with high strength values, such as a high fatigue strength under reverse bending stresses and a high modulus of elasticity. A casing, generally of a metallic material, is associated with the supporting body and functions as wear protection layer and for achieving a low surface roughness and a subsequent surface finish of good surface hardness, for example, by anodizing, without having to fulfill a supporting function. The material of the casing generally has a greater hardness than the material of the supporting body and is correspondingly brittle and has a lower fatigue strength under reverse bending stresses. When used in the intended manner, supporting elements, due to their rapid rotation, are exposed to appreciable alternating bending loads. This frequently leads to breakage of the casing, although the load-carrying capability of the supporting body has not yet been reached. The cracks or breaks thus arising increase the risk of an accident due to cuts. Also, because the material flares at these places, the handling of parts, which are to be pushed on, such as winding tubes or plug-in adapters, which may catch on these flares, is made difficult. Finally, the visual impression of such supporting elements with a damaged casing is not satisfactory. In order to avoid such damage, supporting elements are therefore frequently dimensioned in practice so that, with respect to strength, they are dimensioned for the weakest material, which usually is the casing. With that, the normally higher fatigue strength under repeated reverse bending stresses of the supporting object used cannot be utilized.
It is therefore an object of the invention to provide a generic supporting element, which shows an improved use behavior and, in particular, is damaged less in use, so that the possibility of injury or interference with the handling is reduced.
Since at least one stress-relieving region, extending annularly about the periphery of the casing, is provided as a material-free region or a corresponding region of reduced material thickness, a zone is created there, which makes a selective yielding of the casing possible without the development of undesirable phenomena, such as cracks or material flaring, etc. If the stress-relieving regions are constructed by reducing the thickness of the material of the casing, then the casing, when the maximum fatigue strength under repeated reverse bending stresses of the casing material is exceeded, tears selectively in these regions, which are designed as predetermined breaking points. Due to the lesser thickness of the material in these regions, there is no flaring and there are no sharp, protruding edges. If the casing is provided with one or several material-free regions, which extend annularly about its periphery, the casing pieces, which are formed, are shorter than those formed by a continuous casing. As a result, cracks no longer occur and the casing can be designed so that it withstands the same alternating bending loads that the supporting body withstands.
Further advantages and details arise from the examples of the invention, which are explained in the following and shown in the accompanying drawings.